1. Field of the Invention
The present invention relates to method and apparatus for stably controlling torque of an electric motor driven vehicle, such as an electric vehicle or a hybrid vehicle.
2. Description of the Related Art
Due to increased demand for environment-friendly vehicles, the development of vehicles which have electric motors to generate a drive force has increased. For example, hybrid vehicles use both a gas engine and an electric motor to provide drive force to a vehicle, and electric vehicles or fuel cell vehicles use only electric motors to provide drive force to the vehicles.
The present invention relates to method and apparatus for controlling the torque output from an electric motor of an electric motor driven vehicle, such as a hybrid vehicle, an electric vehicle or a fuel cell vehicle.
Electric motor driven vehicles generally receive drive force from batteries. Therefore, in these types of vehicles, torque from a drive motor must be controlled relative to the SOC (state of charge) of the battery and the current rotational speed of the electric motor. Furthermore, because a point of time of charge and a point of time of generation that pertain to the electric motor vary depending on the state of the battery, the final torque of the drive motor is determined depending on a drive torque limit and a generation torque limit. Therefore, the final torque which is required of the drive motor from the control unit must be determined in the form of an efficient and stable value, taking into account the current rpm of the electric motor, the target torque of the electric motor that is required from a user, a drive torque limit and a generation torque limit of the drive motor depending on the state of the battery or the engine, etc.
However, in the conventional technique, a difference between the drive torque limit and the generation torque limit of the drive motor may become excessively large depending on the operation of the battery or other equipment. In this case, when the drive motor is operated around a section of a boundary between a drive state and a generation state, a phenomenon in which the final torque for controlling the drive motor severely fluctuates occurs. This phenomenon directly affects the stability of the vehicle when driven. Hence, a technique is required, in which the final torque can be always determined in the form of a stable value in the charge section and the discharge section despite sudden changes in surrounding conditions.
It is to be understood that the foregoing description is provided to merely aid understanding the present invention, and does not mean that the present invention falls under the purview of the related art which was already known to those skilled in the art.